1. Field of the Invention
The present invention relates to a sinusoidal signal generating circuit which is used to generate a driving signal for an oscillating element in an angular velocity sensor or the like, and more specifically, to a sinusoidal signal generating circuit which provides a small phase difference with respect to a reference signal and which ensures the minimum generation of noise consisting of high frequency signal components. The present invention also relates to an apparatus for driving an oscillating element with the circuit.
2. Description of the Related Art
FIG. 5A shows an arrangement of a conventional sinusoidal signal generating circuit, and FIG. 5B is a diagram showing the phase delay in the conventional circuit. FIG. 6 conceptually shows an aspect of generating a sinusoidal signal in another conventional sinusoidal signal generating circuit, where V1, V2 and V3 are corresponding input signals and Vo is a sinusoidal output signal.
The sinusoidal signal generating circuit shown in FIG. 5A is constituted by a so called voltage-source-type low pass filter, in which resistors Ra, Rb and capacitors Ca, Cb are associated with an operational amplifier means A1. In the sinusoidal signal generating circuit, a reference signal Vs having a rectangular waveform is supplied to a noninverting input terminal of the operational amplifier Al, and then a sinusoidal output is generated at the output terminal thereof.
On the other hand, three kinds of rectangular signals are used as shown in FIG. 6; an original or source rectangular signal V1, a first reference signal V2 determined by reducing the width of a positive pulse inwards by a predetermined value of time at both the rising edge and falling edge of the source signal, and a second reference signal V3 determined similarly by reducing the width of a negative pulse, and a stepwise output signal Vo exhibiting a pseudo sinusoidal waveform is generated by adding these rectangular signals in a conventional adder (not shown).
However, in the sinusoidal signal generating circuit shown in FIG. 5, the reference signal Vs passes through a low pass filter consisting of a resistor and a capacitor, so that the resistance of the resistor and the capacitance of the capacitor change when the temperature around the circuit varies. As a result, the shape of the output signal Vo is deformed and the output signal Vo after the temperature variation has a phase delay with respect to the output signal Vo at the ordinary temperature, as shown in FIG. 5B. In particular, a phase difference sensing type angular velocity sensor has a limited tolerance regarding the phase difference between the reference signal and the output signal, and therefore the sensor cannot be used as such a sinusoidal signal generating circuit.
Moreover, in the circuit arrangement shown in FIG. 6, the sinusoidal output signal is generated as a pseudo sinusoidal signal consisting of stepwise signals by adding a plurality of rectangular signals. Hence, there always exist rising edges and falling edges in a waveform of the output signal, and the number of these edges increases with the increase of the resolving power. Noise N containing spike-like high frequency signal components often occurs at each edge, and an undesirable effect due to the noise signal extends to the other parts of the circuit arrangement.
If, moreover, the output signal generated by the circuit arrangement in FIG. 6 passes through a low pass filter, the above-mentioned high frequency signal components can be rejected. Nevertheless, the problem regarding the phase difference due to the temperature variation still remains unchanged.
The present invention aims to solve the above-mentioned problems in the prior art, and it is an object of the present invention to provide a sinusoidal signal generating circuit, which ensures minimal phase delay with respect to a reference signal.
Moreover, it is another object of the invention to provide a sinusoidal signal generating circuit, which ensures the minimum generation of noise containing the high frequency signal components.
Furthermore, it is another object of the present invention to provide an apparatus for driving a vibrating element with the above-mentioned circuit for generating a sinusoidal signal.
To attain the above objects, the present invention offers a sinusoidal signal generating circuit comprising a capacitor for charging and discharging, a charging unit for supplying a predetermined charging current to the capacitor and a discharging unit for discharging the discharging current from the capacitor, whereby an output signal is generated by altering the potential of the capacitor, wherein the charging unit includes a charging current adjusting unit for adjusting the magnitude of the discharging current, wherein the discharging unit includes a discharging current adjusting unit for adjusting the magnitude of the discharging current, and wherein a control signal generating means for supplying a plurality of control signals to both the charging current adjusting unit and the discharging current adjusting unit is disposed.
In accordance with the present invention, the charging/discharging of a capacitor is carried out by combining two different discharging currents with two different charging currents, thereby making it possible to vary the potential of the capacitor in various slopes and to produce a pseudo sinusoidal signal by combining the various slopes of the potential.
In the above circuit arrangement, the control signal generating means preferably consists of at least more than one divider for dividing the frequency of the reference signal, a pause duration determining circuit for suppressing the output signal of the dividers for a determined duration in such a manner that control signals do not change, a logic circuit for generating the control signals in a predetermined timing from the signals supplied from the dividers and the pause duration determining circuit.
In the circuit arrangement, it is possible to preset the timing for switching over the charging currents and the discharging currents in such a manner that the signal output approaches a sinusoidal signal.
Moreover, even if the resistance and capacitance are altered, due to, for instance, a temperature variation, no change in the timing for switching over the charging currents and discharging currents arises, thereby making it possible to generate a highly accurate sinusoidal signal without any phase delay.
Moreover, the charging current adjusting unit and the discharging current adjusting unit are each constituted by a plurality of resistors for adjusting the magnitude of currents in a constant current circuit, and a switching means for switching the connections of the resistors, whereby the switching means is preferably controlled by the control signal generating means.
In this case, the slope in the potential variation of the capacitor is determined by a time constant, which is given by a product of the magnitudes of both the resistance of the resistor and the capacitance of the capacitor.
In the above circuit arrangement, the slope of a sinusoidal signal can be preset by changing the time constant of the circuit in which the charging current and discharging current flow.
Furthermore, the charging unit and the discharging unit are each constituted by a current mirror circuit.
In the above circuit arrangement, the charging current to the capacitor and the discharging current therefrom can each be set with a constant current, thereby making it possible to vary the potential of the capacitor in a predetermined slope.
In the above circuit arrangements, moreover, it is preferable to dispose a clamp circuit for clamping an extreme positive or negative value of at least a sinusoidal output to a predetermined voltage value.
Since the extreme positive or negative value of the sinusoidal signal can be set as a fixed value in the above circuit arrangement, the sinusoidal signal can be confined within a fixed amplitude. As a result, the sinusoidal signal can be treated within a predetermined dynamic range, and the center of the amplitude of the sinusoidal signal is preset to a predetermined value.
Moreover, it is preferable to dispose a temperature correcting means for adjusting the magnitudes of both the charging current and discharging current in accordance with the temperature variation.
In the circuit arrangement, it is possible to fix the magnitudes of both the charging current and discharging current into corresponding predetermined values, thereby being able to always obtain a sinusoidal signal having a predetermined amplitude.
In accordance with the present invention, furthermore, an apparatus for driving a vibrating element includes the vibrating element for supplying two output signals at a given angular velocity, said phases of output signals being different from each other, a digitizing means for converting the two output signals into corresponding binary signals in accordance with the polarity of amplitude in the output signals, a phase difference sensing unit for supplying a pulse signal corresponding to a differential signal by determining the phase difference between the two output signals, a low pass filter for generating a control signal from the pulse signal, a voltage controlled oscillator for providing an oscillation having a frequency in accordance with the control signal, a divider means for generating a divided signal having a predetermined frequency by dividing the reference signal supplied from the voltage control oscillator, and a driving means for generating a driving signal for the vibrating element from the divided signal. In the apparatus for driving the vibrating element, it is possible to use the above-mentioned sinusoidal signal generating circuits as the divider means and the driving means.